Generally, the paging procedure of the RANAP protocol is performed as follows. That is, when a paging command is transmitted from a core network (CN) including a mobile switching center (MSC) to a radio network controller (RNC), the radio network controller, in response to the command, performs a paging processing for simultaneously calling a mobile station. In this case, if the range of common ID, that is, the number of mobile stations which the system accommodates, is large, a large amount of processes is incurred at the radio network controller. For this reason, reduction of the amount of processes has been a concern for years.
Accordingly, a method is considered in which the amount of processes is reduced by improving the process of searching for connections based on the RRC (Radio Resource Control) protocol (hereinafter referred to as “RRC connection”), which is performed based on the common ID at each time of paging. The common ID is identification information for identifying a mobile station.
An example of the common ID is IMSI (International Mobile Subscriber Identifier). IMSI is four bytes in length and therefore has a maximum value of 232 (approximately 4.3×109). Thus, searching IMSI at each time of paging incurs a considerably large load.
FIG. 1 shows a conventional paging message (paging message from a core network to a radio network controller, hereinafter referred to as “paging message (core to base)”). According to the conventional paging procedure, upon receiving a paging message (core to base), the radio network controller transmits the paging message via a radio paging control channel (PCCH) or a dedicated control channel (DCCH).
In this case, in order to determine whether to use the radio paging control channel or the dedicated control channel for transmission, the radio network controller searches whether an RRC connection has already been established for a targeted receiving mobile station using a common ID in the message as a key. A paging message (paging message from the radio network controller to the mobile station, hereinafter referred to as “paging message (base to mobile)”) is transmitted via the paging control channel if an RRC connection has not been established and via the dedicated control channel if an RRC connection has been established. This is because although the paging message (base to mobile) is transmitted via the radio paging control channel to a mobile station that is not busy in a communication, a mobile station that is busy in a communication does not allow the message to be received via the paging control channel and thus the paging message (base to mobile) must be transmitted via the dedicated control channel using an RRC connection that has already been established.
Next, the above paging processing will be described with further reference to FIGS. 2 and 3.
FIG. 2 is a diagram showing a paging sequence by which a paging processing is performed to simultaneously call a mobile station 300 from a core network 100 via a radio network controller 200. Referring to the figure, it is to be assumed that the core network 100 includes a mobile switching center that is not shown, and a connection is set up between the mobile switching center and the radio network controller 200 by the SCCP (Signalling Connection Control Part) protocol. The radio network controller 200 controls base stations that are not shown, and a connection is set up between the base stations and the mobile station 300 based on the RRC protocol.
Referring to the figure, a paging message (core to base) 11 of the RANAP protocol is transmitted from the core network 100 to the radio network controller 200 by the connectionless SCCP protocol. It is to be assumed that the paging message (core to base) 11 includes a common ID for identifying a mobile station.
The radio network controller 200 searches whether an RRC connection has already been set up for the mobile station 300 designated by a common ID information element in the paging message (core to base) 11. In this case, the search is performed using a table shown in FIG. 3, that is, a table indicative of associations between common IDs and RRC connections (step 21 in FIG. 2).
Referring now to FIG. 3, for example, if the common ID 0x11110000, “RRC connection is absent” and “search fails” (indicated by a x mark), and a paging 1 message (base to mobile) 12 of the RRC protocol is transmitted to the mobile station 300 via the paging control channel PCCH. Hereinafter, the paging 1 message (base to mobile) transmitted via the paging control channel PCCH will be referred to as “paging 1 message (PCCH).” If the common ID 0x111100011 “RRC connection is present” and “search succeeds” (indicated by a circle mark). It is to be assumed that if “search succeeds,” information indicating which RRC connection is relevant is written in the table (not shown). A paging 2 message (base to mobile) 13 is transmitted using a dedicated control channel DOCCH identified by the search result. Hereinafter, the paging 2 message (base to mobile) transmitted via the dedicated control channel DCCH will be referred to as “paging 2 message (DCCH).”
Next, the core network 100 will be described. The radio network controller 200 can be connected to two types of core network as follows:
(1) Separated Core Network
Nodes with packet service function and nodes with circuit service function are physically separated.
(2) Combined Core Network
Packet service function and circuit service function are combined within a single node. Furthermore, the combined core networks are divided into two types as follows depending on the presence/absence of co-ordination function:
(2.1) Combined Core Network without Co-Ordination Function
Packet service function and circuit service function physically reside within a single node. However, the functions operate individually.
(2.2) Combined Core Network with Co-ordination Function
Packet service function and circuit service function are coordinated.
The combined core network with co-ordination function is capable of recognizing whether a mobile station that is targeted by a paging request already has an RRC connection. For example, when a request for receiving a circuit switched call is issued to a mobile station, within the core network, a circuit service function unit is capable of querying a packet service function unit as to whether a packet call is currently established. It is determined that an RRC connection has been established if a packet call has already been established and that an RRC connection has not been established if a packet call has not been established.
As shown in FIG. 4, SCCP resides in a layer above MTP (Message Transfer Part) and below RANAP. SCCP services are either “connectionless,” in which a connection is not set up and a communication is performed on a one-time basis, or “connection oriented,” in which a connection is set up in advance and a communication is performed using the connection that has been set up.
In the paging sequence described above, even if the core network determines “RRC connection is present,” no means are provided to transmit it to the radio network controller. Accordingly, the radio network controller performs a search using the common ID unconditionally in response to a paging request. Thus, the paging procedure at the radio network controller suffers from the drawback that a large amount of processes is incurred in order to search for the common ID.
Prior arts related to the present invention are known. For example, Japanese Unexamined Patent Publication Tokkai No. Hei 1-316050 achieves, by improving an application for a switch, a connection method with immediacy for a connection between a calling subscriber and a receiving subscriber who is called. However, the publication only discloses technical ideas regarding a system for calling a receiving subscriber with a pager, and is completely different from the present invention, which relates to a simultaneous call for finding the location of a mobile station from base stations.
Also, Japanese Unexamined Patent Publication Tokkai No. Hei 9-168053 discloses a method for communicating maintenance information to a remote apparatus including a remote processor and a pager circuit. However, the publication is also completely different from the present invention, which relates to a simultaneous call for finding the location of a mobile station from base stations.
The present invention has been made in order to overcome the drawback of the conventional art described above, and an object thereof is to provide a radio network controller that serves to reduce the amount of processes for searching for a common ID in a paging procedure, and a paging system and a paging method using the same.